Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
  • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
  • B27K3/02—Processes; Apparatus
  • B27K3/0278—Processes; Apparatus involving an additional treatment during or after impregnation
  • B27K3/0285—Processes; Apparatus involving an additional treatment during or after impregnation for improving the penetration of the impregnating fluid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
  • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
  • B27K3/02—Processes; Apparatus
  • B27K3/08—Impregnating by pressure, e.g. vacuum impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
  • B27K2200/00—Wooden materials to be treated
  • B27K2200/30—Multilayer articles comprising wood
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
  • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
  • B27K3/02—Processes; Apparatus
  • B27K3/04—Impregnating in open tanks

Definitions

• This invention is directed to an improved method for compression impregnating wood veneer with water borne chemical agents. More specifically, this invention is directed to the treating of wood veneers comprising passing multiple layers of the veneer between compression rollers while submerged in a solution of the treating compound.
• the veneers are fed into the compression rollers parallel to the grain or cell orientation and are compressed by the rollers perpendicular to the grain to about one-half of their original thickness.
• the veneers have an original moisture content above the fiber saturation point before compression.
• plywood is a superior wood product when compared to other wood products.
• Plywood has near uniformity in strength properties in the direction of its two major axes and has increased resistance to end checking and splitting and a greatly reduced tendency to twist and warp.
• This superiority of plywood is largely due to the manner in which plywood is constructed.
• Wood is an exceedingly anisotropic material with its flexural strength perpendicular to the grain being about one-fourth of the flexural strength in the direction of the grain.
• the shrinkage and swelling of wood are highly directional. Plywood, by changing the grain direction of successive layers by 90°, minimizes these variations. Therefore, plywood is a highly desirable wood product.
• Stamm process Another drawback of the Stamm process is that the green veneer must be clarezed to remove water from the green veneer before it is passed through the compression rollers which are submerged in the treating solution.
• the wood According to Stamm, the wood must not have water concentrations greater than the fiber saturation point. If the water concentration is greater than the fiber saturation point, then Stamm teaches that both the amount and rate of solution takeup are reduced.
• Most green veneer have water concentrations which are appreciably above the fiber saturation point. Therefore, it is necessary in the Stamm process to pass the green veneer through a pair of hot drying rollers to squeeze out the free water (above fiber saturation point) prior to passing the veneer through the rollers located in the treating bath. It is also necessary to remove this excess water from the preseezer by blowing hot air over the wood surface at the point where the veneer passes between the rollers of the relieveezer. This treatment step is also costly and time consuming.
• the knot occurence in veneer depends on the species from which the veneer is cut, the grade of logs peeled and the depth in the log from which the veneer came. In some species there will be several knots per square foot whereas in others there will be only several knots in a 4 feet ⁇ 8 feet sheet. However, there are very very few sheets without knots.
• veneers cut from spruce logs contain a very large number of knots often averaging several per square foot of veneer. These knots are small but cruse very easily when the sheets of veneer are compressed between steel rollers.
• Southern pine veneers also contain a large amount of knots most of which are relatively large in size. The large knots are always damaged when compressed between hard rollers. Because of the knot problem and the other drawbacks mentioned above, the use of compression treatment with rollers has not heretofore found commercial use for the treatment of veneers.
• the method of my invention comprises passing multiple layers of green veneer between compression rollers while submerged in a solution of the water borne chemicals.
• the veneers must be fed into the squeeze rollers parallel to the grain of the veneer and compressed perpendicular to the grain to about one-half of their original thickness.
• the veneers must have an original moisture content above the fiber saturation point.
• the veneers may be recycled or subjected to several rollers to increase the preservative retention.
• the method of my invention overcomes the prior art problem of knot crushing.
• the use of multiple layers of veneers eliminates the problem of knot crushing. By placing at least one veneer on top of another and compressing at least two layers of veneer at a time I have been able to eliminate the problem of knot crushing.
• the use of multiple layers also increases the production rate.
• treating the veneers in this multiple layers fashion has little or no effect on the solution retention or distribution. Evaluation of veneers treated according to my invention indicate that the treatment is excellent.
• strength tests show the modulus of elasticity and modulus of rupture to be unaffected by the compression impregnation process.
• multiple layers of veneer are very important and critical to the present invention to use multiple layers of veneer. If multiple layers are not employed the benefits of the invention are not realized. By multiple layers is meant more than one layer of veneer.
• the maximum number of layers that my be effectively compressed in accordance with this invention will depend upon such factors as the thickness of the individual veneers, the species of veneer wood, the treating agent and the degree of treatment retention desired. However, for all practical purposes the number of layers of veneer will seldom if ever exceed 5. The most practical number of layers of veneer and hence the preferred number of layers is 2 or 3.
• the use of the multiple layers of veneer does not materially affect the treatment of the veneer. All of the board surfaces of the various veneer layers are effectively treated by the process of my invention.
• my invention comprises simultaneously compressing more than one layer of veneer between compression rollers while the veneers are submerged in a solution of the water borne preservative. It is very important that the veneers are submerged in the treating solution when they emerge from the compression rollers. Therefore, it is not necessary that the compression rollers are completely submerged in the treating solution so long as the veneers are submerged when they emerge from the squeeze rollers.
• the rollers may be located at the water air interface with the downward side of the rollers being submerged.
• the easiest way of making sure the veneers are submerged when they emerge from the squeeze rollers is to have the compresion rollers stragetically located under the solution of water borne chemical agents. Most often at least the bottom roller will be submerged so that the emerging veneers will be under 3 or 4 inches of treating solution.
• the veneer It is critical to the operation that the veneer be submerged as it emerges from the compression rollers.
• the thickness recovery of the veneer after compression is almost instantaneous.
• the veneer recovers from 95 to 97 percent of the original thickness within about 5 seconds after compression. It is during this recovery of thickness that the preservative solution becomes impregnated in the veneer. Therefore, the veneer must be submerged as it emerges from the compression roller and maintained submerged for at least 5 seconds. It is desirable to maintain the veneers submerged for time periods up to 1 minute for maximum retentions. If the veneer is allowed to recover its thickness before being submerged in the water borne preservative solution it takes several hours and in the case of some species of wood several days before sufficient treatment is accomplished.
• the direction of feed of the veneer must be parallel to the grain or cell orientation on the veneer.
• the compressive force must be exerted perpendicular to the grain or cell orientation. It is also desirable that the veneer enter the rollers at about right angles to the opening between the rollers. This prevents damage to the wood and reduces curling in the thinner veneers.
• Another very important variable in the process of my invention is the moisture content of the veneer at the time of compression.
• the moisture content must be above the fiber saturation point. I have found that the higher the moisture content of the veneer before squeezing the greater the retention which will be obtained. This is in direct opposition of the prior art which expressly teaches that the drier the timber the more readily it reassumes its original shape in the presence of the impregnating liquid and the more rapid and complete is the impregnation. See for example, Stamm, U.S. Pat. No. 2,350,135 and Phillips et al, British Pat. No. 597,383.
• the moisture content must be higher than the fiber saturation point ( ⁇ 30-35 percent by weight). It is preferred that the wood have a moisture content of greater than 45 percent. In fact, I have obtained excellent results with wood veneer having a moisture content of higher than 70 percent.
• the rate of feed through the rollers is limited only by the retention time desired in the treating solution tank. As mentioned above, it is necessary to maintain the veneers submerged for a least about 5 seconds as they emerge from the compression rollers. However, it is preferred to maintain them submerged for at least about 10 to 30 seconds. In some cases it is desirable to maintain the veneers submerged for several minutes for maximum retention. There is no critical maximum amount of time for keeping the veneers submerged. If the veneer is kept submerged for more then 1 minute additional retention may result due to normal soaking effects.
• the additional compressions increase the preservative retention.
• Each additional pass through submerged compression rollers will increase the original retention by about 10-20 percent.
• the maximum retentions obtainable depend on the particular species of wood being treated and will generally be within the range of 30 to 35 pounds of solution per cubic foot of wood.
• the additional compression steps may be performed by recycling the veneer through the same set of rollers. However, it is preferred to use several sets of rollers when additional compression is desirable. Generally, it will be desirable to use two sets of rollers. In addition it will seldom be necessary to pass the veneer between more than 3 sets of compression rollers.
• the green veneers should be compressed to at least about one-half of their original thickness in order to obtain the desired retention. If only a small amount of retention is desirable, then the amount of compression may be reduced. Veneers of thickness up to about 1/8 inch may be compressed to 1/2 of their original thickness without much difficulty. However, thicker veneers, especially hardwood veneers, are sometimes more difficult to compress to this extent. Additional passes through compression rollers will compensate for the reduced compression on the thicker veneers. If a series of compression rollers are used, each successive pair of rollers may be set to compress the veneers an increasing amount to reduce the load on the first set of rollers and assist in obtaining higher retentions.
• the limit in the thickness of veneers which can be compression impregnated depends on the compressibility of the particular species of wood being processed. Softer woods will allow thicker veneers to be processed. For example, double layers of 1/8 inch spruce veneers were treated by the compression impregnation process of my invention without any difficulty. However, double layers of 1/8 inch lauan veneers split when compressed to 1/2 of their original thickness.
• the compression impregnation process of my invention may be used to treat all the various species of veneer wood which are used to make plywood.
• My invention will work on both hardwood and softwood veneers. Examples of some of the commercially used veneer wood in the United States are: Ash, Beech, Birch, Cedar, Cherry, Elm, Fir, Maple, Oak, Pine, Poplar, Redwood, Spruce, and Walnut.
• my invention will work on the foreign woods which are being used to make plywood.
• the compression impregnation process of my invention may be used to treat veneers with all types of water solutions and suspensions of treating agents.
• the method may be used for preservatives, fungicides, fire retardants, water repellents and resins which impart dimensional stability, acid resistance and hardness.
• the veneer samples were about 6 inches wide and 12 inches long.
• the veneers were passed through a set of steel compression rollers.
• the veneers were treated in double layers, one layer of veneers being placed directly on top of another layer of veneer.
• the veneers were under several inches of treating solution when they emerged from the rollers.
• the veneers were kept submerged in the solution for about 10 seconds.
• the initial moisture content of the veneers was about 70 percent.
• the treated veneers were chemically analyzed to determine the pounds per cubic foot retention of chemical solution.
• the chemical solution was a 2.7 percent solution of WOLMAN CCA preservative salts. The results are shown in Table 1 below.
• Table 1 demonstrate the effectiveness of my invention.
• the veneers treated by compression inpregnation retained a sufficient amount of treatment chemicals.
• each additional pass through the compression rollers increased the previous retention by about 10 percent.
• a visual inspection of the treated veneers showed that all knots were intact and not damaged in any manner.
• a sample of spruce sapwood veneer treated in a manner similar to that described above, except the veneer was treated in a single layer resulted in irreparable damage to the knots and the surrounding wood.
• a series of Douglas fir, birch and spruce veneers were treated with a solution of NON-COM Exterior fire retardant chemicals (proprietary product of Koppers Co., Inc. ) by the compression impregnation process of this invention.
• the treated veneers were dried, cured, and laid up into five ply plywood samples. These plywood samples were tested for fire retardant properties and strength properties.
• the fire tube test results showed that the compression impregnation method of this invention yields treated plywood having very satisfactory fire resistant properties.
• the results of the strength tests showed that there was no significant difference between plywood made with compression impregnated veneers and plywood made with uncompressed veneers.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Forests & Forestry (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)

Priority Applications (17)

Applications Claiming Priority (1)

Publications (1)

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Cited By (5)

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Citations (14)

• 1973
  • 1973-11-07 US US05/413,524 patent/US3950577A/en not_active Expired - Lifetime
• 1974
  • 1974-02-20 CA CA193,080A patent/CA1009519A/en not_active Expired
  • 1974-02-21 GB GB801474A patent/GB1451822A/en not_active Expired
  • 1974-02-22 DK DK97574AA patent/DK140656B/da unknown
  • 1974-02-26 ES ES423634A patent/ES423634A1/es not_active Expired
  • 1974-02-28 IE IE00424/74A patent/IE39021B1/xx unknown
  • 1974-03-01 LU LU69518A patent/LU69518A1/xx unknown
  • 1974-03-04 IT IT48938/74A patent/IT1015828B/it active
  • 1974-03-04 SE SE7402818A patent/SE397938B/xx unknown
  • 1974-03-04 NL NL747402883A patent/NL152788B/xx unknown
  • 1974-03-05 FI FI646/74A patent/FI56497C/fi active
  • 1974-03-05 NO NO740764A patent/NO135233C/no unknown
  • 1974-03-08 FR FR7408062A patent/FR2249751B1/fr not_active Expired
  • 1974-03-22 BE BE142373A patent/BE812733A/xx unknown
  • 1974-03-27 JP JP49034323A patent/JPS5071805A/ja active Pending
  • 1974-06-28 BR BR5373/74A patent/BR7405373A/pt unknown

Patent Citations (14)

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